The present invention relates generally to apparatus for applying print to the exterior surfaces of tubes and, more particularly, is directed to a tube orienting mechanism for orienting the tubes with respect to a printing blanket such that printing on the tubes always occurs at the same circumferential position thereof.
In general, a variety of machines for applying a decorative print to containers, such as tubes and the like, are known. Such machines generally include an infeed conveyor assembly that transports the tubes to a positioning unit that receives the tubes and moves them into position for transfer to corresponding mandrels located on a rotatable mandrel wheel. After the tubes are received on the corresponding mandrels, the mandrels are rotated into position for the printing operation, whereby a printing blanket is brought into contact with each of the tubes, to place a decorative finish on the outer cylindrical surfaces thereof. Thereafter, the mandrels bearing the tubes are moved to another location where the tubes are dried and then to still another location where a coat of varnish is applied to the decorated outer surface of each tube to finish the decoration thereon. The varnish is then cured at a subsequent station and the tubes are thereafter removed from the mandrel wheel.
With such apparatus, it is necessary to orient the tubes with respect to the printing blanket so that the decorative print is always applied at the same position on the tubes. In this regard, a tube printing apparatus sold by Mall GmbH in Germany includes an orienting head which engages the tube then in contact with the printing blanket. Once the blanket makes contact with the tube, the orienting head backs out and the tube is rotated and printed by the printing blanket. Specifically, the orienting head is controlled to intermittently reciprocate to thereby engage the tube then at the printing station, and is also controlled to continuously rotate to thereby rotate the engaged tube.
In order to provide synchronization between movement of the printing blanket and the orienting head, a separate drive is provided for the orienting head. Specifically, a synchronous motor is used which brings the orienting head up to the surface speed of the printing blanket. A problem with such arrangement, however, is in providing accurate synchronization of the orienting head and the printing blanket. Generally, this must be performed electronically and becomes relatively complex. Furthermore, over periods of time, because of the two different drive systems, movement of the printing blanket and the orienting head move out of phase with each other, resulting in a loss of synchronization.
This loss of synchronization requires stopping of the apparatus to correct the same which, as aforesaid, is relatively complex and which results in down time of the machine. More importantly, because of the two drive system, there is a limiting speed of operation of the apparatus. For example, the Mall printing apparatus is generally limited to printing at the rate of 110 tubes per minute, since otherwise, the apparatus will not orient properly, that is, will not be synchronously timed. This speed limiting factor is inefficient and costly.